Sheet metal structure



y 1947; J/B. CASTLE 2,423,682

SHEET METAL STRUCTURE FiledMay so, 1944 2 Sheets-Sheet 1 Join B. Ca slleIN V EN TOR.

ATTORNEY July 8, 1947. J. B. CASTLE SHEET METAL STRUCTURE Filed'May 30,1944 2 Sheets-Sheet 2 Ja/m 5 @5276 INVENTOR.

Y v BY 7 g '55 ATTQRNEK Patented July 8, 1947 SHEET METAL STRUCTURE JohnB. Castle, Los Angeles, Calif., assignor to Douglas Aircraft Company,Inc., Santa Monica,

Calif.

Application May 30, 1944, Serial No. 538,023

' 2 Claims. 1

My invention relates to a method and means of stifiening thin sheets ofmetal or other comparatively rigid material, and specifically to thestiffening of beams having thin webs of the type commonly used inaircraft construction, as for instance to constitute wing ribs, andparticularly relates to the strengthening of such thin metal sheets whenprovided with flanged lightening holes.

As is well known, beams having webs of thin sheet material, particularlywhen the web is rela-' tively deep, are liable to fail under heavy loadsby buckling of the web. For this reason wing ribs formed as beams ofthin sheet metal are commonly stiffened by the addition of verticalstiffening members extending across the web. While beams having thinwebs provided with flanged lightening holes are much stiffer, weight forweight, than beams not so constructed, nevertheless failure will alsooccur when the calculated maximum load is approached or passed bybuckling of the web to the side to which the flanges are carried.

It is the general object of the invention to provide a method and meansof increasing the stiffness of a sheet metal member without increasingthe weight of the member.

An object of the invention is to provide a method and means ofconstruction to increase the strength of beams with thin metal websprovided with flanged lightening holes without increasing the weight ofthe beam by pressing stiffening elements from the material of the webbetween adjacent flanged lightening holes or cutouts.

It is a further object of the invention to provide beams of the kinddescribed in the form of Wing ribs having lightening holes andstrengthening elements without increase in the weight of the ribsbecause of the presence of the strengthening elements, saidstrengthening elementsbeing pressed out of the material of the Web onthe opposite side to that to which the flanges of the lightening holesare carried. An additional object is toprovide a wing rib in which theflanges of the lightening holes and the stifiening elements extend inopposite directions, so that loadings can be carried well in excess ofthose that can be carried by beams not so constructed.

Further objects and features of the invention will hereafter appear inthe following description and accompanying drawings in which a preferredembodiment of the invention is described by way of example, but it is tobe understood that this illustrative showing is not in any waylimitative of the scope of the invention which is defined by theappended claims.

In the drawings, in which identical reference numerals indicateidentical parts in the several figures:

Figure 1 is a side elevation of a beam having a thin sheet web providedwith flanged lightening holes and incorporating the construction of myinvention.

Figure 2 is a cross section taken on the line 2-2 of Figure 1.

Figure 3 is a broken cross section on the line 3-3 of Figure 2.

Figure 4 is a side elevation of another form of beam having a thin sheetmetal Web provided with flanged lightening holes, one of which iscircular and another of which comprises straight sides joined by arcs ofa circle, and also including the construction of my invention.

Figure 5 is a cross section on the line 55 of Figure 4.

Figures 6 and '7 are diagrammatic views illustrating the deflection of abeam with a thin metal web provided with lightening holes, but notincluding the construction of my invention.

Figures 8 and 9 are diagrammatic views similar to Figures 6 and 7 of abeam construction including the construction of my invention.

In the drawings HI indicates a beam of relatively light sheet metal ofthe type used to form the rib members of airplane wings. The thin webportions of such ribs are commonly provided with lightening holes formedby punching out material and forming the material surrounding the holeto provide a flange having a generally angular cross section with oneelement of the flange parallel to the face of the web. These flanges ofthe hole are made as deep as possible without unduly stretching thematerial of the web. The beam comprises flange portions l2 and webportion M, the beams being provided with flanged lightening holes Hi,the flanges l8 of which are carried to the same side as the flanges l2.Such a beam, while stiff for its weight, will nevertheless fail ifloading in the face plane 26 0f the web is carried to a high enoughvalue, by buckling toward the side to which the flanges of thelightening holes are carried out. I have discovered and verified bynumerous tests that the beam can be strengthened so as to have almosttwice the strength of a beam of the known construction by providingstiifening elements between adjacent lightening holes as indicated at22, these stiffening elements being pressed out of the web to rise fromthe opposite side to that to which the flanges of the lightening holesare carried. The strengthening elements are formed so that they extendfrom a root portion 24 merging with th web portions of the heel or bendline tangent to top and bottom of adjacent lightening holes to a crownportion 25 which is positioned at a point intermediate the adjacentlightening holes in a zone through which passes the line joining thecenters of the circles defining circular lightening holes. Theconstruction appropriate to lightening holes not formed as true circlesis described withreference to Figure 4. It will be noted that thestrengthening element increases continuously in height from the rootportion 2A to the crown portion 26, this increase of height of thestrengthening element preferably following a straight line. The effectof this construction is to provide crowned trengthening columns in theweb of the beam. Loads W applied .as indicated by the arrows in Figure 2tend to cause the flanges of the lightening holes to move away from theplane of-the face of the web 20 and to cause the formed web intermediatethe lightening holes to move in the opposite direction and thereby toincrease the depth of the beam resulting in an increase in the moment ofinertia of the beam, thus increasing the resistance to deflection of thebeam. The comparative behavior of a beam formed as a rib of sheet metalhaving flanged lightening holes of usual construction is shown inFigures 6 and 7, the deflection of the beam under load W being indicatedby dotted lines. It will be noted that the cross section of the beam hasbecome more shallow under load, reducing its moment of inertia, andtherefore its stability has been decreased which will result in failureby buckling under heavy load, whereas in a beam construction accordingto my invention, as diagrammatically illustrated in Figures 8 and 9, thedeflection of the beam under load W is such that while the web may bendto deflect to the side of the flanged edges of the lightening holes,such deflection is resisted by the crowned column, while if the webtends to deflect to the side on which the crowned column is positioned,this tendency is resisted by the flanges of the lightening holes.

Figure 4 shows the manner of forming the strengthening elements arrangedbetween lightening holes having straight side portions or betweenlightening holes of circular form and such holes having straight sideportions. The end of the root portion of the strengthening element asbefore described lies along a heel line tangent to the upper and lowerarcs defining the lightening holes. The increase of depth of thestrengthening element however, should not be carried past the point atwhich the straight portions of the lightening holes become tangent tothe arcs joining the straight portions. The crown of the strengtheningmember is therefore flat toward the lightening hol 28 which comprisesstraight side portions'Bll joined by arcs 32, this straight portionextending from point 34 to 39. On the side toward the circularlightening hole 33 the crown of the stiffening member will lieapproximately at the point 40.

The height of the crown portion of the stiffening element above the planof the sheet is preferably approximately half the depth of thelightening hole flange.

A generally satisfactory spacing of the lightening holes in the web of athin sheet metal rib is such that adjacent hole are apart by slightlymore than th depth of the flanged lightening hole, the width of thecrown of the stiffening column occupying the whole distance betweenadjacent holes.

Where the width of the stiffening elements toward the heel lines tangentto the periphery of adjacent lightening holes is such'as to leaverelatively large areas of sheet metal, it is advantageous to press outor otherwise form a pillow or stiffening depression as is standardpractice instiffening such areas.

It has been found that where a structural member of the kind to whichthe invention relates is subjected to exceptionally high shear stresses,stiffening may be effected according to my invention although materialis not removed from dished out stiffening depressions to form lighteningholes, said additional material serving to increase the shear strengthof the member.

It is pointed out that it is immaterial whether the beam is formed witha flange integral with the web as in the rib construction described byway of illustration, or formed with separate flange members betweenwhich a thin web formed according to my invention is positioned, as forinstance by riveting it to top and bottom flanges. It has been found asa result of test, that the portion of the beam of my invention mostliable to failure is at the point of connection of the flange and weband not in the web.

Various embodiments of the invention other than that described will beevident to those skilled in the art and Various changes may be made inthe form and arrangement of my invention for stiffening thin sheets ofrigid material Without departing from the scope of my invention asdefined by the appended claims.

I claim:

1. A beam having a web of sheet material provided with flangedlightening holes arranged in a juxtaposed series in the web, the flangesof said holes projecting angularly from said web and terminating in aninwardly directed annular member substantially parallel to said Web; andcolumns, arranged between adjacent flanged lightening holes, projectingto the side opposite to that to which the flanges of said lighteningholes project, said columns rising from the face plane of said web fromlines tangent to the top and bottom peripheries of adjacent flangedlightening holes to a crown intermediate the length of said columns.

2. A beam having a web of sheet material provid-ed with flangedlightening holes arranged in a juxtaposed series in the web, the flangesof said holes projecting angularly from said web and terminating in aninwardly directed annular member substantially parallel to said web; andcolumns, arranged between adjacent flanged lightening holes, projectingto the side opposite to that to which the flanges of said lighteningholes project, said columns rising from the face plane of said web fromlines tangent to the top and bottom peripheries of .adjacentflangedlightening holes to a crown intermediate the length of'said columns, theheight of each column at the crown portion thereof being equal tosubstantially-half the distance between the inwardly directed-annularmember and said web.

JOHN B. CASTLE.

REFERENCES CITED The following references are of record in the file ofthis patent:

Great Britain Aug. 28,1919

